TTBandpassButterworth2.cpp

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/** @file
 *
 * @ingroup dspFilterLib
 *
 * @brief #TTBandpassButterworth2 is a second-order Butterworth bandpass filter.
 *
 * @details Butterworth filters have maximum flat frequency response in the pass band.
 *  Based on an algorithm from Dodge & Jerse (1997): Computer Music -
 *  Synthesis, Composition, and Performance. 2nd edition. Schirmer.
 *
 * @authors Trond Lossius, Timothy Place,
 *
 * @copyright Copyright © 2008, Trond Lossius @n
 * This code is licensed under the terms of the "New BSD License" @n
 * http://creativecommons.org/licenses/BSD/
 */


#include "TTBandpassButterworth2.h"

#define thisTTClass         TTBandpassButterworth2
#define thisTTClassName     "bandpass.butterworth.2"
#define thisTTClassTags     "dspFilterLib, audio, processor, filter, bandpass, butterworth"


TT_AUDIO_CONSTRUCTOR
{
    // register attributes
    addAttributeWithSetter(Frequency,       kTypeFloat64);
    addAttributeProperty(Frequency,         range,          TTValue(10.0, sr*0.45));
    addAttributeProperty(Frequency,         rangeChecking,  TT("clip"));

    addAttributeWithSetter(Q,               kTypeFloat64);

    // register for notifications from the parent class so we can allocate memory as required
    addUpdates(MaxNumChannels);
    // register for notifications from the parent class so we can recalculate coefficients as required
    addUpdates(SampleRate);
    // make the clear method available to the outside world
    addMessage(clear);

    // Set Defaults...
    setAttributeValue(kTTSym_maxNumChannels,    arguments);         // This attribute is inherited
    setAttributeValue(TT("frequency"),      1000.0);
    setAttributeValue(TT("q"),              50.0);
    setProcessMethod(processAudio);
    setCalculateMethod(calculateValue);

}


TTBandpassButterworth2::~TTBandpassButterworth2()
{
    ;
}


TTErr TTBandpassButterworth2::updateMaxNumChannels(const TTValue& oldMaxNumChannels, TTValue&)
{
    mX1.resize(mMaxNumChannels);
    mX2.resize(mMaxNumChannels);
    mY1.resize(mMaxNumChannels);
    mY2.resize(mMaxNumChannels);    
    clear();
    return kTTErrNone;
}


TTErr TTBandpassButterworth2::updateSampleRate(const TTValue& oldSampleRate, TTValue&)
{
    TTValue v(mFrequency);
    return setFrequency(v);
}


TTErr TTBandpassButterworth2::clear()
{
    mX1.assign(mMaxNumChannels, 0.0);
    mX2.assign(mMaxNumChannels, 0.0);
    mY1.assign(mMaxNumChannels, 0.0);
    mY2.assign(mMaxNumChannels, 0.0);
    return kTTErrNone;
}


TTErr TTBandpassButterworth2::setFrequency(const TTValue& newValue)
{
    mFrequency = newValue;
    calculateCoefficients();
    return kTTErrNone;
}


TTErr TTBandpassButterworth2::setQ(const TTValue& newValue)
{
    mQ = newValue;  
    calculateCoefficients();
    return kTTErrNone;
}


void TTBandpassButterworth2::calculateCoefficients()
{   
     
    // Avoid dividing by 0
    if (mQ > 0.1)
        mBw = mFrequency/mQ;
    else
        mBw = mFrequency;
        
    mC = 1. / tan( kTTPi*(mBw/sr) );
    mD = 2. * cos( kTTTwoPi*(mFrequency/sr) );
    mA0 = 1. / (1. + mC);
    // a1 = 0.
    mA2 = -mA0;
    mB1 = mA2 * mC * mD;
    mB2 = mA0 * (mC - 1.);
}


inline TTErr TTBandpassButterworth2::calculateValue(const TTFloat64& x, TTFloat64& y, TTPtrSizedInt channel)
{
    y = mA0*x + mA2*mX2[channel] - mB1*mY1[channel] - mB2*mY2[channel];
    TTZeroDenormal(y);
    mX2[channel] = mX1[channel];
    mX1[channel] = x;
    mY2[channel] = mY1[channel];
    mY1[channel] = y;
    return kTTErrNone;
}


TTErr TTBandpassButterworth2::processAudio(TTAudioSignalArrayPtr inputs, TTAudioSignalArrayPtr outputs)
{
    TT_WRAP_CALCULATE_METHOD(calculateValue);
}